Structure and method for enhancing resistance to fracture of bonding pads

ABSTRACT

The present invention provides bond pads structures between semiconductor integrated circuits and the chip package with enhanced resistance to fracture and improved reliability. Mismatch in the coefficient of temperature expansion (CTE) among the materials used in bond structures induces stress and shear on them that may result in fractures within the back end dielectric stacks and cause reliability problems of the packaging. By placing multiple metal pads which are connected to the bond pad through multiple metal via, the adhesion between the bond pads and the back end dielectric stacks is enhanced.

FIELD OF THE INVENTION

The present invention relates to semiconductor structures, andparticularly, to bonding pad structures.

BACKGROUND OF THE INVENTION

In the semiconductor industry, a bond pad refers to a contiguous metalpad typically formed out of the last layers of metal during asemiconductor manufacturing sequence. A bond pad is typically largeenough to accommodate the bottom portion of a solder ball. A bond padstructure refers to a structure containing such a bond pad andsurrounding or attached structure, which as a whole helps accommodatethe solder ball.

Once the fabrication of integrated circuit elements on a semiconductorsubstrate is completed, the semiconductor substrate is diced andpackaged in a bonding process. Bond pads provide a structure forelectrical connection between the fabricated integrated circuit elementsand the package. Typically, one end of an interconnection wire is bondedto a bond pad and the other end is bonded to the next level ofintegration, which is typically an inner lead of the package. In atypical bonding process, multiple interconnection wires are utilized toconnect each of the electrically active pads to one of the inner leadsof the package.

A typical bond pad structure contains an exposed large piece of metal onwhich a bonding wire is attached with a solder ball. During theoperation of the chip, the temperature of the chip rises, therebyraising the temperature of the bonding structure including the bondingpad and the solder ball. Due to the differences in the coefficients ofthermal expansion (CTE), the bonding structure is subjected to shear andstress. These may cause cracks in the bonding structure causingelectrical failure of the bonding pad or slow degradation andreliability problems due to ingress of ambient atmosphere, especiallymoisture into the chip. Wakharkar et al., “Materials Technologies forThermomechanical Management of Organic Packages,” Vol. 09, Issue 04,November 2005, pp. 309-324” discusses various aspects of reliability dueto chip-package interaction (CPI).

Therefore, mechanical strength of the bonding structure that issufficient to withstand the stress and shear during the operationallifetime of a chip is of utmost importance in the design of a bondingstructure. To establish the reliability of a particular bond structure,it is customary in the semiconductor industry to subject the bondstructures to rigorous stress routines and measure their failure rate.The standard method of testing the mechanical strength of a bondingstructure is known as “JEDEC Standard” and is widely used in thesemiconductor industry.

Many designs to enhance the mechanical strength of the bonding structureare known. As an example, U.S. Pat. No. 6,365,970 to Tsai et al.; U.S.Pat. No. 5,739,587 to Sato; and U.S. Pat. No. 5,700,735 to Shiue et al.utilize multiple layers of metals and via plugs. These structuresutilize multiple layers of metals connected with via plugs in thebonding pad area to mechanically strengthen the bonding structures. Onedisadvantage of this approach is the lack of availability of the bondingpad area for wiring purposes. In other words, since multiple metallevels are filled with structures that are part of the bond structure,no other electrical structure such as metal wiring can be built withinthe same space. Thus, metal wiring is severely limited under the bondpad.

An alternative approach in the prior art that maximizes the availablespace for wiring under the bond pad is also known. Instead of utilizingmultiple layers of metal, only the top level of metal is utilized forthe bond pad. An electrical connection from the bond pad to lower metallevels is provided through an extension of the bond pad and viasattached to a lower level metal wire. The area below the bond pad isavailable for electrical wiring. If electrical wiring is not neededunder the bond pad, the area in the lower level under the bond pads maybe filled with metal fills to facilitate a chemical mechanicalplanarization (CMP) process.

It has been discovered during the process of the present invention thatthe above structure with one level of metal for the bond pads is proneto fracture when subjected to reliability stress. While the structureabove provides maximum flexibility for wiring, the mechanical strengthof the structure is not sufficient to provide a reliable structure understress.

Therefore, the need exists to provide a bond pad structure that providessufficient mechanical strength while still providing as much flexibilityin metal wiring under the bond pad structure as possible.

SUMMARY OF THE INVENTION

The present invention addresses the needs described above and provides abond pad structure with enhanced mechanical strength. Specifically, thepresent invention aims to increase the mechanical strength of a bond padstructure compared to the prior art that maximizes the available spacefor wiring under a bond pad.

The present invention also provides as much free space as possible undera bond pad structure to facilitate the ease of design for wiringpurposes.

Furthermore, the present invention provides a bond pad structure thatfacilitates easy manufacture of the structure without excessive burdenon process control. Specifically, the present invention seeks to placemetal fills as necessary under a bond pad structure to reduce dishingduring a chemical mechanical polishing process during the manufacture ofthe structure.

While this disclosure uses specific materials to describe the invention,it should be recognized that functionally equivalent material may besubstituted for any of the material described below.

In accordance with one aspect of the present invention, multiple firstmetal vias are placed within the “pad area”, that is, within theboundaries of a first metal pad, or a bond pad, and adjoined to the bondpad from below. Each of the multiple first metal vias are connected tomutually disjoined multiple metal pads, herein referred to as “multiplemetal pads,” which are located below the multiple first metal vias. Eachof the multiple metal pads are confined within the metal levelimmediately below the level of the bond pad itself.

In this inventive structure, not only does the bottom surface of thebond pad itself adhere to the insulating layer immediately below, butthe walls of the multiple first metal vias and all the surfaces of themultiple metal pads not adjoining the multiple first metal vias alsoadhere to the dielectrics surrounding them. The area of adhesion betweenthe dielectric material in the back end of the line film stack and thecontiguous and conducting extension of the bond pad, including the bondpad itself, the multiple first metal vias, and the multiple metal pads,is increased significantly.

In accordance with another aspect of the present invention, the use ofmetal wiring in the area within the metal levels below the bond pad isenabled to provide enhanced flexibility in metal wiring. The metalwiring may be utilized to pass current from another part of thesemiconductor chip through the area containing the bond pad to yetanother part of the semiconductor chip. The area not utilized by themultiple metal pads or by the metal wiring may be filled with metalfills to facilitate the chemical mechanical planarization process duringthe manufacturing. Alternatively, if the area below the bond pad is notutilized, metal fills only may be utilized to facilitate the CMPprocess.

While small portions of the multiple pads may actually be locatedoutside the pad area, the multiple metal pads and the multiple firstmetal vias landing on them are substantially within the pad area tominimize the adverse impact on the wiring. The multiple metal pads maybe confined exclusively within the peripheral area, defined as the areawithin the pad area and along the periphery of the bond pad, or they maybe confined exclusively within the center area, defined as the remainderof the center area after excluding the peripheral area. Alternatively,the multiple metal pads may be distributed across the pad area, bothwithin the peripheral area and within the center area.

In accordance with yet another aspect of the present invention, aportion of the pad area within the metal level below the bond pad,wherein the multiple metal pads are located, may be utilized toelectrically connect the bond pad to the integrated circuit elements onthe chip and to provide enhanced flexibility in metal wiring. The use ofadditional metal wire connected to the bond pad has the advantage ofreducing the resistance of the electrical path from the bond pad,thereby reducing a voltage drop between the bond pad and the integratedcircuit elements.

In this case, the unused portion of the pad area within the metal levelbelow the bond pad may also be utilized for a second set of metal wiresfor passing current from another part of the semiconductor chip throughthe pad area within the metal level below the bond pad to yet anotherpart of the semiconductor chip. If some unused area still remains in thepad area within the metal level below the bond pad, metal fills mayoptionally be used to facilitate the CMP process.

According to still another aspect of the present invention, multiplefirst metal vias are placed within the “pad area”, that is, within theboundaries of a first metal pad, or a bond pad, and adjoined to the bondpad from below. Each of the multiple first metal vias are connected toone of mutually disjoined multiple metal stacks, herein referred to as“vertical alternating stacks,” wherein third metal pads and second metalvias are alternately adjoined to one another. When two components of avertical alternating stack are adjoined, they are always adjoinedvertically, that is, one on top of another. The top of each of thevertical alternating stack is a third metal pad which adjoins the bottomof at lease one of the multiple first metal vias. All components withineach vertical alternating stack are electrically connected to oneanother.

Not only does the bottom surface of the bond pad itself adhere to theinsulating layer immediately below in this structure, but the walls ofthe multiple first metal vias and surfaces of all the verticalalternating stacks not adjoining the multiple first metal vias alsoadhere to the dielectrics surrounding them. The area of adhesion betweenthe dielectric material in the back end of the line film stack and thecontiguous and conducting extension of the bond pad, including the bondpad itself and the multiple vertical alternating stacks, is increasedsignificantly.

A portion of pad area within the metal level below the bond pad, whereinthe multiple metal pads are located, may be utilized to electricallyconnect the bond pad to the integrated circuit elements on the chip andto provide enhanced flexibility in metal wiring in this structure. Also,the unused portion of the pad area within the metal level below the bondpad may also utilized for a second set of metal wires for passingcurrent from another part of the semiconductor chip through the pad areawithin the metal level below the bond pad to yet another part of thesemiconductor chip. If some unused area still remains in the pad areawithin the metal level below the bond pad, metal fills may optionally beused to facilitate the CMP process.

The adhesion between the bond structures according to the variousaspects of the present invention is superior to prior art structureswithout any via below a bond pad while the flexibility of wiring isbetter than prior art structures wherein the bond pad structure occupiesmultiple levels of metal layers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a top-down view of a bond pad structureaccording to the prior art.

FIG. 2 is a schematic diagram of a cross-sectional view of a bond padstructure in FIG. 1 in the direction A-A′.

FIG. 3 is a scanning electron micrograph (SEM) of a structure accordingto the prior art showing a fracture induced during the preconditioningof JEDEC level 3 test.

FIG. 4 is a magnified view of the scanning electron micrograph (SEM) inFIG. 3 of the area with the fracture.

FIG. 5 is a schematic diagram of a top-down view of a bond pad structureaccording to a first embodiment of the present invention.

FIG. 6 is a schematic diagram of a cross-sectional view of a bond padstructure in FIG. 5 in the direction B-B′.

FIG. 7 is a schematic diagram of a top-down view of a bond pad structureaccording to a second embodiment of the present invention.

FIG. 8 is a schematic diagram of a cross-sectional view of a bond padstructure in FIG. 7 in the direction B-B′.

FIG. 9 is a schematic diagram of a top-down view of a bond pad structureaccording to a third embodiment of the present invention.

FIG. 10 is a schematic diagram of a cross-sectional view of a bond padstructure in FIG. 9 in the direction B-B′.

FIG. 11 is a schematic diagram of a top-down view of a bond padstructure according to a fifth embodiment of the present invention.

FIG. 12 is a schematic diagram of a cross-sectional view of a bond padstructure in FIG. 11 in the direction B-B′.

FIG. 13 is a schematic diagram of a top-down view of a bond padstructure according to a seventh embodiment of the present invention.

FIG. 14 is a schematic diagram of a cross-sectional view of a bond padstructure in FIG. 13 in the direction B-B′.

FIG. 15 is a schematic diagram of a top-down view of a bond padstructure according to an eighth embodiment of the present invention.

FIG. 16 is a schematic diagram of a top-down view of a bond padstructure according to a ninth embodiment of the present invention.

FIG. 17 is a schematic diagram of a cross-sectional view of a bond padstructure in FIG. 13 in the direction B-B′.

DETAILED DESCRIPTION OF THE INVENTION

Before describing the present invention in detail, a discussion of aprior art bond pad structure is provided. The purpose of this discussionis to clearly illustrate the fundamental difference between the priorart and the present invention.

Referring to FIG. 1, a schematic top-down view of a prior art bond padstructure 100 is provided wherein a bond pad 150, a bond pad extension151, a portion of a metal wire 120 that is electrically connected to thebond pad 150 and to the bond pad extension 151 through two vias 156 areshown. Also shown are the opening 161 in a passivation layer 160 (notshown in FIG. 1) and in a photosensitive polyimide layer 170 (not shownin FIG. 1) as well as the periphery 181 of a barrier liner material 180(not shown in FIG. 1). A metal fill 121 within the area of the bond padextension 151 is shown as well as multiple metal fills 123 within thearea of the pad 150, or the “pad area.”

FIG. 2 is a schematic cross-sectional view of the prior art bond padstructure 100 along the line labeled A-A′ in FIG. 1. A first insulatinglayer 110, which is the topmost insulating layer from the underlyingback end of the line stack, contains the metal wire 120 as well as themetal fill 121 under the bond pad extension 151 and the metal fills 123contained within the pad area. While additional metal fills are notspecifically shown under the bond pad 150, they may be placed in thesame level as the metal fill 121 shown in FIG. 2. Disposed on top of thefirst insulating layer 110 is a second insulating layer 135, which inturn comprises a cap layer 130, and an insulating dielectric layer 140.A bond pad 150 and the bond pad extension 151 are disposed on top of thesecond insulating layer 135. A via 156, which is filled with metal andelectrically connects the bond pad extension 151 and the metal wire 120insulating layer, is disposed within an opening in the second insulatinglayer 135 and the cap layer 130. A passivation layer 160 and aphotosensitive polyimide layer 170 are disposed over the bond pad 150,the bond pad extension 151, or the second insulation layer 135. Theopening 161 in the passivation layer 160 and a photosensitive polyimidelayer 170 is also shown. The barrier liner material 180 and itsperiphery 181 and the solder is disposed over the opening 161. A solderball 190 is disposed on the barrier liner material 180.

In the course of experiments leading to the present invention, the priorart bond pad structures schematically represented by FIGS. 1-2 weremanufactured and placed under reliability stress conditions.Specifically, these samples were subjected to the JEDEC level 3 testingwherein each package formed using a bonding process on the bond pads issubjected to preconditioning and then tested for functionality for thenext 168 hours. In other words, certification at JEDEC level 3 testingmeans that the package can operate for 168 hours after being subjectedto preconditioning. The preconditioning method for level 3 JEDEC testingis 192 hours of exposure to 60% relative humidity at 30 degree Celsius.

Some of the samples showed structural fails after the preconditioningstress. FIG. 3 shows a scanning electron micrograph (SEM) 300 of across-section of one of the samples that failed after thepreconditioning stress. With a rotation of a solder ball 390, or a “C4ball,” due to the shear and stress during the preconditioning, theunderlying back end of the line stack 310 separated from the solder ball390 causing a crack 399 between them. The location of the crack isschematically shown in FIG. 2 as a dotted line 199.

FIG. 4 shows a magnified SEM 400 of the SEM 300 shown in FIG. 3, whereinthe structures surrounding the crack 499 are shown in more detail. Afirst insulating layer 410, which is the topmost insulating layer in theback end of the line stack (not fully shown in FIG. 4) and is a TEOS(Tetra Ethyl Orthosilicate; (C₂H₅O)₄Si) based FSG (Fluorosilicate Glass)in this SEM, contains metal fills 423 in the pad area. The metal fills423 are made of copper in this case. One part of a stack, consisting ofa portion 430 of a cap layer, which in turn contains an NBLoK (NitridedBarrier Low K: nitrogen doped silicon carbide (SiN_(X)C_(Y)H_(Z)) asexemplified in U.S. Pat. No. 7,009,280) and a nitride layer, and aportion 440 of a second insulating layer, is attached to the firstinsulating layer 410 above. Another part of the same stack, consistingof a different portion 431 of the cap layer and a different portion 441of the second insulating layer, is attached to an aluminum alloy 450below. A crack 499 between the two parts of the same stack is clearlyvisible and is located between the first dielectric 410 above and thealuminum alloy 450 below. The aluminum alloy 450 comprises a liner stackand aluminum in this particular case. The liner stack is made oftantalum nitride (TaN), titanium (Ti), and titanium nitride (TiN). Belowthe aluminum alloy 450 is a passivation layer 460, of which a crack isvisible in this SEM 400. The passivation layer 460 is a stack of oxideand nitride in this case. Below the passivation layer 460 is a polyimidelayer 470. Part of the solder ball 490 is also seen.

Clearly, the mechanical strength of this structure was not sufficient toprevent the delamination of the bond pad structure from the underlyingback end of the line dielectric material during the preconditioning. Asshall be seen below, the present invention strengthens the mechanicalstrength of a bond pad structure to prevent fails as seen in FIGS. 3-4.

According to a first embodiment of the present invention, a first bondpad structure 500 is described in FIGS. 5-6. FIG. 5 is a schematictop-down view, while FIG. 6 is a schematic cross-sectional view alongthe line B-B′ in FIG. 5. The first bond pad structure 500 has a firstmetal pad 550, which is a bond pad, in the first layer of the structure.The area inside the periphery of the first metal pad 550 is referred toas the “pad area.” Only one contiguous first metal pad is necessary forthe formation of one of the first bond pad structure 500. The firstmetal pad 550 is made of metal, and preferably a stack of a linermaterial and an aluminum alloy. A bond pad extension 551, adjoining thebond pad 550, built on the same level as a bond pad 550, and consistingof the same material as the bond pad, may optionally be constructed aswell. The liner material may comprise a stack of tantalum nitride (TaN),titanium (Ti), and titanium nitride (TiN) or an alternate stack ofmetals with good adhesion property to the underlying dielectricmaterial.

The first bond pad structure 500 according to the first embodiment ofthe present invention contains a first insulating layer 535 disposedunderneath the first metal pad 550 and extends at least over the entirepad area. The bottom surface of the first metal pad 550 adjoins the topsurface of the first insulating layer 535. In FIG. 6, the firstinsulting layer 535 comprises a stack of an insulating dielectric layer540 disposed on top of a cap layer 530, both of which are insulators.Preferably, the insulating dielectric layer 540 is chosen from a siliconoxide layer, a silicon nitride layer, and a doped silicon oxide layersuch as a fluorosilicate glass (FSG). Preferably, the cap layer 530 ischosen from a BLoK layer (a Barrier Low K layer as exemplified in U.S.Pat. No. 6,632,478), an NBLoK layer, and a silicon nitride layer.Alternatively, the first insulating layer 535 may comprise a singlelayer of insulating material or even a stack of more than two insulatingmaterials.

The first bond pad structure 500 according to the first embodiment ofthe present invention contain multiple first metal vias 552 through thefirst insulating layer 535 and are located within the pad area. The topsurface of each of the multiple first metal vias 552 adjoins a portionof the bottom surface of the first metal pad 550, or the bond pad.Optionally, metal vias 556 may be utilized to connect the bond padextension 551 to a portion of a metal wire 520 below. Preferably, thefirst metal vias 552 and the first metal pad 550 are aluminum alloys.Most preferably, the first metal vias 552 and the first metal pad 550are formed at the same time as a stack containing a liner material andaluminum.

The first bond pad structure 500 according to the first embodiment ofthe present invention contains multiple metal pads 522 disposedunderneath the first insulating layer 535, and overlapping at least aportion of the pad area, and not adjoined to one another. The multiplemetal pads 522 are located beneath the multiple first metal vias 552 andadjoin the bottom surface of at least one of the multiple first metalvias 552. The multiple metal pads 522 are placed within a secondinsulating layer 510 disposed below the first insulating layer 535 suchthat at least a portion of the top surface of the second insulatinglayer 510 adjoins a portion of the bottom surface of the firstinsulating layer 535. Preferably, the multiple metal pads 522 arecontained within the pad area to reduce the area from which furthermetal wiring needs to be excluded. Optionally, metal fills 521 may beplaced under the bond pad extension 551. Preferably, the multiple metalpads 522 are copper alloys. Most preferably, the multiple metal pads 522contain a liner material and copper.

Furthermore, the location of the multiple first metal vias 552 islimited in the first embodiment of the present invention. To qualifythis limitation some definitions are presented below:

The center point 555 of the first metal pad 550 is defined as follows.For each of the points within the top surface of the first metal pad,the maximum distance to the periphery of the first metal pad ismeasured. In other words, each point within the first metal pad isassigned a number which corresponds to the maximum distance to theperiphery, or the boundary, of the first metal pad 550. The point thatachieves the minimum number among all the numbers assigned to the pointswithin the first metal pad is defined as the center point 555 of thefirst metal pad 550.

To define a boundary 557, each point on the periphery of the bond pad550 is hypothetically connected by a straight line to the center point555. At a fixed percentage of the distance between 15% and 85% measuredfrom the center point 555, each of the hypothetical straight lines isterminated. The set of all the terminated points define the boundary557.

The pad area of the first metal pad 550 is divided into two areas, aperipheral area 559 located between the periphery of the bond pad 550and the boundary 557, and a center area 558 confined within the boundary557. While in all passages below, whenever the peripheral area isdescribed as “an area inside and along edges of said first metal pad” orin similar wordings, the rigorous definition as described above applies.While different percentage numbers may be selected to define a boundary557 for a given metal pad 550, that is, any percentage between 15% and85%, one boundary has one number for the selected percentage.

According to the first embodiment of the present invention, the centerarea 558 does not contain any second metal pad 522. All the metal padsare confined within the peripheral area 559. Consequently, all of thefirst metal vias 552 are also located within the peripheral area 559.

The first bond pad structure 500 according to the first embodiment ofthe present invention may further contain a passivation layer 560, whichis disposed on the first metal pad 550, the bond pad extension 551, andthe first insulating layer 535. The passivation layer 560 blocks theingress of moisture from the ambient environment into the integratedsemiconductor elements below the first bond pad structure 500.Preferably, the passivation layer 560 comprises a silicon nitride or astack of dielectric material containing silicon nitride, such as a stackof silicon nitride and silicon oxide. Furthermore, a photosensitivepolyimide (PSPI) 570 may be disposed on the passivation layer 560.Alternatively, a different material that can be lithographicallypatterned and conducive to the bonding process may be utilized.

The first bond pad structure 500 according to the first embodiment ofthe present invention may further contain an opening 561 through boththe passivation layer 560 and the PSPI 570. Also, it may contain abarrier layer material 580 with the periphery 581 and disposed on top ofthe first metal pad 550 within the area of the opening 561. A solderball 590 may be placed on the barrier layer material 580.

The second metal pads 522 have bottom surfaces, sidewall surfaces, andtop surfaces that are not covered by the multiple first metal vias 552.This increases the area of the interface between the first bond padstructure 500 and the surrounding insulating material. Furthermore, thebottom surfaces and the sidewall surfaces of the second metal pads 522may have a liner material with good adhesion to the insulating material,as is typically the case in typical semiconductor processing flow.Therefore, the adhesion of the first bond pad structure 500 issignificantly higher than that from the bond pad structure 100 in FIGS.1-2 known in the prior art, resulting in higher mechanical strength andimproved reliability of the structure under stress.

Typical bond pads are made of an aluminum alloy while most of metalwiring within the back end of the line dielectric stack utilizes copper.The higher adhesion strength between copper and dielectric material thanthat between the aluminum alloy and dielectric material is utilized inthe bond pad structure according to the present invention.

While the area of adhesion is significantly increased, a substantialportion of the area in the metal levels below the bond pad itself isstill available for metal wiring. While the flexibility of metal wiringis less than that of a prior art bond pad structure without any viasbelow the bond pad and thus has maximal available wiring pace under thebond pad, considering that such a structure is prone to reliabilityissues, a moderate decrease in the flexibility of metal wiring is afully warranted tradeoff in engineering. The advantage of the structureaccording to the present invention in maintaining good flexibility inwiring is apparent in comparison with other prior art structures.

According to the second embodiment of the present invention, a secondbond pad structure 700 is described in FIGS. 7-8. FIG. 7 is a schematictop-down view, while FIG. 8 is a schematic cross-sectional view alongthe line B-B′0 in FIG. 7. The second bond pad structure 700 according tothe second embodiment of the present invention is similar to the firstbond pad structure 500 according to the first embodiment of the presentinvention and shares many of the same features. Consequently, likeelements between the first and the second embodiments of the presentinvention are numbered the same. Furthermore, in all of the additionalembodiments to be described below, like elements between the describedembodiment of the present invention and the first embodiment of thepresent invention share the same numbers in figures.

According to the second embodiment of the present invention, the centerarea 558 of the bond pad structure 700 does not contain any second metalpad 522. All the metal pads are confined within the peripheral area 559.All of the first metal vias 552 are also located within the peripheralarea 559. Furthermore, at least one metal structure that does notcontact any of the first metal vias 552 is placed within the pad areaand at the same level as the second metal pads 522. The metal structurecan be either first metal fills 523 or at least one first metal wire525. None of the first metal fills 523 or any of a portion of the firstmetal wires 525 is adjoined by any of the first metal vias 552. In otherwords, there are no metal vias within the pad area that connect any ofthe metal fills 23 or any of a portion of the first metal wires 525 tothe first metal pad 550 above.

Any of the first metal wires 525 may extend outside the pad area to makeelectrical connections to other components of the integrated circuit asnecessary. The first metal wires 525 may be utilized to make electricalconnections to various parts of the integrated circuit elements or toany other pad other than the bond pad 550, or even to the bond pad 550through secondary connections. However, there is no first metal via 552that connects the bond pad 550 and any of the first metal wires 525directly.

The second embodiment of the present invention enables the placement offirst metal wires 525 under the first metal pad 550, or the bond pad, toutilize the area for increased flexibility in wiring during the circuitlayout compared to the first embodiment of the present invention. Theunused areas after the placement of a portion of the first metal wires525 are filled with first metal fills 523.

According to a third embodiment of the present invention, a third bondpad structure 900 is described in FIGS. 9-10. FIG. 9 is a schematictop-down view, while FIG. 10 is a schematic cross-sectional view alongthe line B-B′ in FIG. 9. The second bond pad structure 900 according tothe third embodiment of the present invention is similar to the firstbond pad structure 500 according to the first embodiment of the presentinvention.

According to the third embodiment of the present invention, theperipheral area 559 of the bond pad structure 900 does not contain anysecond metal pad 522. All the metal pads are confined within the centerarea 558. Consequently, all of the first metal vias 552 are also locatedwithin the center area 559. The third embodiment of the presentinvention shares the advantages of the first embodiment of the presentinvention with the difference being that the area that may be utilizedfor other purposes within the pad area and at the same level as thesecond metal pads 522 coincide with the peripheral area 559 instead ofthe center area 558.

According to a fourth embodiment of the present invention, a fourth bondpad structure is derived from the third bond pad structure 900 in FIG.9. All structural features according to the third embodiment of thepresent invention are also present in the fourth embodiment of thepresent invention as well. The additional features of the fourthembodiment compared to the features of the third embodiment are similarto the additional features of the second embodiment compared to thefeatures of the first embodiment. For this reason, elements in FIGS. 7-8are used in this passage to describe the additional features of thefourth embodiment compared to the third embodiment of the presentinvention. According to the fourth embodiment of the present invention,at least one metal structure that does not contact any of the firstmetal vias 552 is placed within the pad area and at the same level asthe second metal pads 522. The metal structure can be either first metalfills 523 or at least one first metal wire 525. None of the first metalfills 523, nor any of a portion of the first metal wires 525 areadjoined by any of the first metal vias 552. In other words, there areno metal vias within the pad area that connect any of the metal fills 23or any of a portion of the first metal wires 525 to the first metal pad550 above.

The fourth embodiment of the present invention enables the placement offirst metal wires 525 under the first metal pad 550, or the bond pad, toutilize the area for increased flexibility in wiring during the circuitlayout compared to the first embodiment of the present invention. Theunused areas after the placement of a portion of the first metal wires525 are filled with first metal fills 523. The difference between thefourth embodiment and the second embodiment of the present invention iswhether the peripheral area 559 or the center area 558 is used for theplacement of the second metal pads 552.

According to a fifth embodiment of the present invention, a fifth bondpad structure 1100 is described in FIGS. 11-12. FIG. 11 is a schematictop-down view, while FIG. 12 is a schematic cross-sectional view alongthe line B-B′ in FIG. 11. The fifth bond pad structure 1100 according tothe third embodiment of the present invention is similar to the firstbond pad structure 500 according to the first embodiment of the presentinvention except that both the center area 558 and the peripheral area559 are used for the placement of the second metal pads 552 in the fifthembodiment while only the peripheral area 559 is utilized for theplacement of the second metal pads 552 in the first embodiment of thepresent invention. The fifth embodiment of the present invention enablesan increase in the mechanical strength of the bond pad structure 1100 atthe expense of flexibility in metal wiring in the same level as thesecond metal pads 522 compared to the first embodiment.

According to a sixth embodiment of the present invention, a sixth bondpad structure is derived from the fifth bond pad structure 1100 in FIG.11. All structural features according to the fifth embodiment of thepresent invention are also present in the sixth embodiment of thepresent invention as well. As in the description of the fourthembodiment of the present invention above, elements in FIGS. 7-8 areused in this passage. According to the sixth embodiment of the presentinvention, at least one metal structure that does not contact any of thefirst metal vias 552 is placed within the pad area and at the same levelas the second metal pads 522. The metal structure can be either firstmetal fills 523 or at least one first metal wire 525. None of the firstmetal fills 523, nor any of a portion of the first metal wires 525 areadjoined by any of the first metal vias 552. In other words, there areno metal vias within the pad area that connect any of the metal fills 23or any of a portion of the first metal wires 525 to the first metal pad550 above.

The sixth embodiment of the present invention enables the placement ofat least one first metal wire 525 under the first metal pad 550, or thebond pad, to utilize the area for increased flexibility in wiring duringthe circuit layout. The unused areas after the placement of a portion ofthe first metal wires 525 are filled with first metal fills 523. Thedifference between the sixth embodiment and the second or fourthembodiment of the present invention is whether both the peripheral area559 and the center area 558 are used for the placement of the secondmetal pads 552 or only one of the two areas is used for the samepurposes.

According to a seventh embodiment of the present invention, a seventhbond pad structure 1300 is described in FIGS. 13-14. FIG. 13 is aschematic top-down view, while FIG. 14 is a schematic cross-sectionalview along the line B-B′ in FIG. 13. The seventh bond pad structure 1300according to the seventh embodiment of the present invention shares allthe elements of the first bond pad structure 500 according to the firstembodiment of the present invention described above. In addition, atleast one second metal wire 524 is placed within the pad area and at thesame level as the second metal pads 522. Any of the second metal wires524 may extend outside the pad area to make electrical connections toother components of the integrated circuit as necessary. All of thesecond metal wires 524 is adjoined by at least one of the first metalvias 552 and electrically connected to the bond pad.

The seventh embodiment of the present invention enables the use of thepad area at the same level as the second metal pads for wiring the bondpad 550 to the integrated circuit elements below. Alternatively, thesecond metal wires 524 may be used with existing wiring scheme to reducethe resistance of the circuit wiring path from the bond pad 550.

According to an eighth embodiment of the present invention, an eighthbond pad structure 1500 is described in a schematic top-down view inFIG. 15. The eighth bond pad structure 1500 according to the presentinvention shares all the elements of the seventh bond pad structure 1300according to the seventh embodiment. Furthermore, at least one metalstructure that does not contact any of the first metal vias 552 isplaced within the pad area and at the same level as the second metalpads 522. The metal structure can be either first metal fills 523 or atleast one first metal wire 525. None of the first metal fills 523, norany of a portion of the first metal wires 525 are adjoined by any of thefirst metal vias 552. In other words, there are no metal vias within thepad area that connect any of the metal fills 23 or any of a portion ofthe first metal wires 525 to the first metal pad 550 above. Thestructure and the functionality of the first metal wires 525 is exactlythe same as described in any of the prior embodiments of the presentinvention.

The eighth embodiment of the present invention enables the placement offirst metal wires 525 under the first metal pad 550, or the bond pad, toutilize the area for increased flexibility in wiring during the circuitlayout compared to the seventh embodiment of the present invention. Theunused areas after the placement of a portion of the first metal wires525 are filled with first metal fills 523.

Table 1 below shows a list of enabled elements according to the firstthrough eighth embodiments of the present invention in a tabular format.

TABLE 1 List of enabled elements according to the first through eighthembodiments of the present invention First metal First metal vias inSecond vias in center peripheral First metal First metal metal wiresEnabled elements area 558 area 559 fills 523 wires 525 524 Firstembodiment No Yes No No No Second embodiment No Yes Yes Yes No Thirdembodiment Yes No No No No Fourth embodiment Yes No Yes Yes No Fifthembodiment Yes Yes No No No Sixth embodiment Yes Yes Yes Yes No Seventhembodiment No Yes No No Yes Eighth embodiment No Yes Yes Yes Yes

According to a ninth embodiment of the present invention, a ninth bondpad structure 1600 is described in FIGS. 16-17. FIG. 16 is a schematictop-down view, while FIG. 17 is a schematic cross-sectional view alongthe line B-B′ in FIG. 16. Since all elements common with the otherembodiments of the present invention are labeled with the same referencenumber and have the same structural and functional characteristics, onlythe key elements of the ninth embodiment of the present invention aredescribed herein.

The first bond pad structure 500 has a first metal pad 550 and a firstinsulating layer 535. Multiple first metal vias 552 through the firstinsulating layer 535 are located within the pad area wherein the topsurface of each of the multiple first metal vias 552 adjoins a portionof the bottom surface of the first metal pad 550, or the bond pad.

According to the ninth embodiment of the present invention, multiplethird metal pads 502 and multiple second metal vias 507 are provided.Each of the third metal pads 502 may be placed in any metal level belowthe level of the first metal pad 550. The distinction between thirdmetal pads 502 and second metal pads 522 of the previous embodiments(See FIGS. 5-13 and 15)is made herein to point out that the third metalpads 502 may be placed in any metal level below the level of the firstmetal pad 550 whereas the second metal pads 522 of the previousembodiments (See FIGS. 5-13 and 15) can be placed only in the metallevel immediately below the level of the first metal pad 550. Also, eachof the second metal vias 507 may be placed between any two metal levelsor even between a metal level and the semiconductor substrate.

However, each of the third metal pads 502 and each of the second metalvias is a part of one of the many vertical alternating stacks 595, whichis formed alternately adjoining third metal pads and second metal viasvertically such that the component for the top of each verticalalternating stack 595 is one of the third metal pads 502. In otherwords, a vertical alternating stack comprises at least one of thirdmetal pads 502 and at least one of second metal vias 507. The stackingsequence of each of the vertical alternating stacks, counted from thetop to bottom, begins with a third metal pad 502, followed by a secondmetal via 507, and alternates between one of the third metal pads 502and one of the second metal vias 507 if more components are used. If thecomponents of the alternating vertical stacks are listed from top tobottom, for example, an alternating vertical stack may consist of athird metal pad 502 and a second metal via 507, a third metal pad 502and a second metal via 507 and another third metal pad 502, a thirdmetal pad 502 and a second metal via 507 and another third metal pad 502and another third metal via 507, a third metal pad 502 and a secondmetal via 507and another third metal pad 502 and another second metalvia 507 yet another third metal pad, etc. The bottom of a sequence mayterminate with a third metal pad 502 or a second metal via 507. Thebottom of a vertical alternating stack may terminate within a layer ofback end of the line dielectric material, a shallow trench isolation, orthe semiconductor substrate.

Optionally, at least one metal structure that does not contact any ofthe multiple metal vias 552 or any of the vertical alternating stacks595 is placed within the pad area and at any level wherein any of thethird metal pads 502 are located. The metal structure can be eithersecond metal fills 503 or at least one third metal wire 505. Once again,a distinction between embodiments of the present invention is made inthat second metal fills and third metal wires in the ninth embodimentmay be placed at any level wherein any of the third metal pads 502 arelocated whereas first metal fills and first metal wires in the priorembodiments can be placed only in the metal level immediately below thelevel of the first metal pad 550. None of the second metal fills 503, orany of a portion of the third metal wires 505 is adjoined by any of thefirst metal vias 552 or by any of the alternating vertical stacks 595.In other words, there is no electrical connection between the bond pad550 and either the second metal fills 503 or third metal wires 505.

Any of the third metal wires 505 may extend outside the pad area to makeelectrical connections to other components of the integrated circuit asnecessary. The third metal wires 505 may be utilized to make electricalconnections to various parts of the integrated circuit elements or toany other pad other than the bond pad 550, or even to the bond pad 550through secondary connections. However, there is no first metal via 552that connects the bond pad 550 and any of the first metal wires 505directly.

Also, optionally, at least one fourth metal wire (not shown in FIGS.16-17) maybe placed within the pad area and at the same level as any ofthe third metal pads 502. Both structurally and functionally, the fourthmetal wires are similar to the second metal wires 524 as described inthe bond pad structure 1300 according to the seventh embodiment of thepresent invention in FIGS. 13-14. However, the fourth metal wiresaccording to the ninth embodiment of the present invention may be placedin any level containing at least one of the third metal pads 502 whereasthe second metal wires according to the seventh and eighth embodimentsof the present invention limits the placement of the second metal wiresto the metal level immediately below the level of the first metal pad550. Any of the fourth metal wires may extend outside the pad area tomake electrical connections to other components of the integratedcircuit as necessary. All of the fourth metal wires are directly orindirectly adjoined by at east one of the first metal vias 552 andelectrically connected to the bond pad 550.

A method of fabricating the bond pad structures in the variousembodiments described above is now discussed.

Integrated circuit devices are first formed on a semiconductorsubstrate. A back end of the line stack is formed layer by layer abovethe integrated circuit devices by depositing insulator layers, etchingof lines and vias in the insulator layers, filling the metal lines andvias with metal, and removing the excessive metal outside the metallines and planarizing the surface for each layer of processing.

In the case of the ninth embodiment according to the present invention,the vertical alternating stacks 595 are formed within the back end ofthe line stack by forming third metal pads 502 in appropriate metallayers at the same time and using identical processing methods as whenthe metal wires in the same level are formed. Similarly, second metalvias 507 are formed at the same time and using identical processingmethods as when other vias in the same level are formed. Proceeding inthis manner, all components of the vertical alternating stacks 595located below the second insulating layer 510 in the bond pad structure1600 in FIGS. 16-17 are formed.

For all embodiments of the present invention, a second insulating layer510 is deposited over an underlying region of semiconductor device atthis point. The underlying region may have a back end of the line stack,which in turn may comprise multiple insulator layers, metal line levels,and via levels as is necessary for the implementation of the ninthembodiment of the present invention as described above. The second metalpads 522, any of the first metal fills 523, any first metal wires 525,and any second metal wires 524 according to the first through eighthembodiment of the present invention are lithographically patterned onthe second insulating layer 510 by depositing a layer of photoresist,exposing it under a mask to a light source, and developing it.Alternatively, third metal pads 502 and any of the second metal fills503, third metal wires 505, and fourth metal wires that are locatedwithin the bond pad structure 1600 in FIGS. 16-17 according to the ninthembodiment of the present invention are lithographically patterned onthe second insulating layer 510 in a similar manner. The lithographicpattern is then etched into the second insulating layer 510 by areactive ion etch (RIE) process.

Vias located within the second insulating layer 510 are formed bylithographically patterning the vias followed by an etch process thattransfers the pattern into the second insulating layer 510. Patterningand etching of the vias may be performed prior to or after the etchingof the pattern for the second metal pads 522 or the third metal pads 502that are located within the second insulating layer 510. In the ninthembodiment of the present invention, the second metal vias 507 that arelocated within the second insulating layer 510 are formed at the sametime as the other vias located within the same level.

All the features in the metal level within the second insulating layer510 are filled with a first conducting material. Specifically, accordingto the first through eighth embodiments of the present invention, thesecond metal pads 522, any of the first metal fills 523, any first metalwires 525, and any second metal wires 524 are filled with the firstconducting material. Alternatively, according to the ninth embodiment ofthe present invention, the third metal pads 502 and any of the secondmetal fills 503, third metal wires 505, and fourth metal wires that arelocated within the bond pad structure 1600 in FIGS. 16-17 are filledwith the first conducting material. The first conducting metal ispreferably a stack of a liner material and a metal layer. Mostpreferably, the metal layer is made of copper. Preferably, the fillprocess fills both the metal lines and the metal vias at the same time,which is called a dual damascene process.

Any excess first conducting material above the top surface of the secondinsulating layer 510 is then removed by a chemical mechanical polish(CMP) process.

While the process for the manufacture of the structures within thesecond insulating layer 510 is described with a dual damascene processwhether the metal lines be formed first or the vias be formed first, thesame structures may alternatively be fabricated using a single damasceneprocess, wherein the features in the via levels are produced first andthe features in the metal line level are produced thereafter. Thisinvention may be practiced both ways.

Thereafter, a first insulating layer 535 is deposited over the secondinsulating layer 510 and the metal structures filled with the firstconducting material. Preferably, the first insulating layer 535comprises a stack of a cap layer 530, which is deposited first, and aninsulating dielectric layer 540, which is deposited after and on top ofthe cap layer 530.

Another layer of photoresist is deposited over the first insulatinglayer 535, exposed to a light source under a mask, and developed suchthat a pattern of multiple first metal vias 552 are formed on thephotoresist. The pattern includes the features for first metal vias 552.This pattern is etched into the first insulating layer 535 using a RIEprocess. The patterned part of the first insulating layer 535 is etchedthrough and portions of the top surface of the metal structures areexposed. The resulting structure includes openings for the formation ofthe first metal vias 552. Specifically, the exposed metal surfaces arethose of the second metal pads 552 and any of the second metal wires 524in the seventh or eighth embodiment of the present invention or those ofthe third metal pads 552 within the level of the second insulating layer510 and any of the fourth metal wires in the ninth embodiment of thepresent invention.

Thereafter, a metal layer made of a second conducting material isdeposited over the first insulating layer and inside the openings.Preferably, the second conducting material is an aluminum alloy. Mostpreferably, the second conducting material is a stack containing a linermaterial and aluminum. This deposition process forms a blanket film,which includes the first metal pad 550, the first metal vias 552, and anoptional bond pad extension 551 as well as unwanted portions of thesecond conducting material elsewhere.

A third pattern containing a pattern for the first metal pad 550 andoptionally, the bond pad extension 551 is formed by depositing yetanother layer of photoresist, and exposing it to a light source under amask containing the features for the first metal pad 550 and optionalbond pad extension 551. The unwanted portions of the second conductingmaterial that are located outside the area of the first metal pad 550and outside the area of the bond pad extension 551, if any of the bondpad extension 551 is present, is then etched and removed. Thus, theshape of the first metal pad 550, or a bond pad, is defined at thispoint.

Thereafter, a passivation layer 560 is deposited over the first metalpad 550 and over the second insulating layer 535, followed by adeposition of a photosensitive polyimide layer 570 over the passivationlayer 560. The photosensitive polyimide layer 570 is then exposed to alight source under a mask that contains a pattern for an opening 561over the first metal pad 550. A portion of the passivation layer 560 andthe photosensitive polyimide layer 570 is then removed from above thefirst metal pad 550 from within the area of the opening 561. The opening561 within the passivation layer 560 and the photosensitive polyimidelayer 570 is smaller than the size of the first metal pad 550.

While the invention has been described in terms of specific embodiments,it is evident in view of the foregoing description that numerousalternatives, modifications and variations will be apparent to thoseskilled in the art. Accordingly, the invention is intended to encompassall such alternatives, modifications and variations which fall withinthe scope and spirit of the invention and the following claims.

1. A bond pad structure comprising: a first metal pad disposed over apad area; a first insulating layer disposed underneath said first metalpad; a plurality of first metal vias through said first insulating layerand adjoining said first metal pad; and a plurality of verticalalternating stacks of at least one of third metal pads and at least oneof second metal vias, wherein said plurality of vertical alternatingstacks is connected to said first metal pad through said plurality offirst metal vias, wherein each of said vertical alternating stacks islocated beneath said first metal vias, adjoins at least one of saidplurality of first metal vias, and terminates at its top with one ofsaid third metal pads, wherein each of said plurality of verticalalternating stacks does not adjoin any other conducting material thansaid plurality of first metal vias, and wherein an entirety of saidplurality of vertical alternating stacks underlies said pad area of saidfirst metal pad.
 2. A bond pad structure, comprising: a first metal paddisposed over a pad area; a first insulating layer disposed underneathsaid first metal pad; a plurality of first metal vias through said firstinsulating layer and adjoining said first metal pad; a plurality ofvertical alternating stacks of at least one of third metal pads and atleast one of second metal vias, wherein each of said verticalalternating stacks is located beneath said first metal vias, adjoins atleast one of said plurality of first metal vias, and terminates at itstop with one of said third metal pads, and wherein each of saidplurality of vertical alternating stacks does not adjoin any otherconducting material than said plurality of first metal vias; and atleast one portion of at least one first metal wire located beneath saidfirst metal pad and within said pad area and not lower than the lowestpart of any of said vertical alternating stacks, wherein no portion ofsaid at least one first metal wire is adjoined to any of said firstmetal vias or said plurality of vertical alternating stacks.
 3. The bondpad structure of claim 1, further comprising a plurality of metal fillslocated beneath said first metal pad and within said pad area, none ofsaid metal fills being adjoined to any of said first metal vias or saidplurality of vertical alternating stacks.
 4. A bond pad structure,comprising: a first metal pad disposed over a pad area; a firstinsulating layer disposed underneath said first metal pad; a pluralityof first metal vias through said first insulating layer and adjoiningsaid first metal pad; a plurality of vertical alternating stacks of atleast one of third metal pads and at least one of second metal vias,wherein each of said vertical alternating stacks is located beneath saidfirst metal vias, adjoins at least one of said plurality of first metalvias, and terminates at its top with one of said third metal pads, andwherein each of said plurality of vertical alternating stacks does notadjoin any other conducting material than said plurality of first metalvias; and at least one portion of at least one second metal wire locatedbeneath said first metal pad and within said pad area and not lower thanthe lowest part of any of said vertical alternating stacks, wherein noportion of said at least one second metal wire is adjoined to any ofsaid first metal vias or said plurality of vertical alternating stacks.5. The bond pad structure of claim 1, further comprising: a passivationlayer disposed on top of said first metal pad; a photosensitivepolyimide layer disposed on top of said passivation; and an opening overa portion of said first metal pad through said passivation layer andthrough said photosensitive polyimide layer.
 6. The bond pad structureof claim 2, wherein said at least one first metal wire is not directlyadjoined to said plurality of first metal vias or said bond pad.
 7. Thebond pad structure of claim 2, wherein said at least one second metalwire extends outside said pad area to make electrical connections toother components of an integrated circuit.
 8. The bond pad structure ofclaim 2, further comprising a plurality of metal fills located beneathsaid first metal pad and within said pad area, none of said metal fillsbeing adjoined to any of said first metal vias or said plurality ofvertical alternating stacks.
 9. The bond pad structure of claim 2,further comprising a passivation layer disposed on top of said firstmetal pad; a photosensitive polyimide layer disposed on top of saidpassivation; and an opening over a portion of said first metal padthough said passivation layer and through said photosensitive polyimidelayer.
 10. The bond pad structure of claim 5, wherein said at least onesecond metal wire is adjoined by at least one of said plurality of firstmetal vias and electrically connected to said bond pad.
 11. The bond padstructure of claim 5, wherein said at least one second metal wireextends outside said pad area to make electrical connections to othercomponents of an integrated circuit.
 12. The bond pad structure of claim5, further comprising a circuit wiring path connected to said bond pad,wherein said at least one second metal wire reduces resistance of saidcircuit wiring path.
 13. The bond pad structure of claim 5, furthercomprising a plurality of metal fills located beneath said first metalpad and within said pad area, none of said metal fills being adjoined toany of said first metal vias or said plurality of vertical alternatingstacks.
 14. The bond pad structure of claim 5, further comprising: apassivation layer disposed on top of said first metal pad; aphotosensitive polyimide layer disposed on top of said passivation; andan opening over a portion of said first metal pad through saidpassivation layer and through said photosensitive polyimide layer.